Ammonia refrigerating machine, working fluid composition and method

ABSTRACT

The present invention provides a working fluid composition for a refrigerating machine obtained by mixing an ammonia refrigerant with a lubricating oil which is extremely excellent in solubility with the ammonia refrigerant, and a method for lubricating a refrigerating machine suitable for the use of the working fluid composition. 
     The working fluid composition comprises a mixture of ammonia and one or more kinds of polyether compounds represented by the formula (I); the refrigerating machine is characterized by constituting a refrigerating cycle or a heat pump cycle through which the working fluid composition is circulated; and the method for lubricating a refrigerating compressor is characterized by lubricating the ammonia refrigerant compressor with the lubricating oil comprising one or more kinds of ether compounds represented by the formula (I) 
     
         R.sub.1 -- --O--(PO).sub.m --(EO).sub.n --R.sub.2 !.sub.x  (I) 
    
     wherein R 1  is a hydrocarbon group having 1 to 6 carbon atoms, R 2  is an alkyl group having 1 to 6 carbon atoms, PO is an oxypropylene group, EO is an oxyethylene group, x is an integer of from 1 to 4, m is a positive integer, and n is 0 or a positive integer.

This is a continuation application of Ser. No. 08/175,391, filed on Jan.7, 1994, now abandoned.

TECHNICAL FIELD

The present invention relates to a refrigerating machine using arefrigerant mainly comprising ammonia, a working fluid compositioncomprising a mixture of a refrigerant and a lubricating oil for use in aheat pump and the refrigerating machine, and a method for lubricating anammonia compressor.

BACKGROUND ART

Heretofore, Flon has been widely used as a refrigerant for arefrigerating machine and a heat pump (hereinafter referred togenerically as "the refrigerating machine"). However, when dischargedinto the atmosphere, the Flon is accumulated and then decomposed byultraviolet rays of the sun to produce chlorine atoms, and thesechlorine atoms destroy the ozone layer having a function to protect theearth from the intensive ultraviolet rays of the sun. For this reason,the use of the Flon is getting limited. In recent years, much attentionis thus paid to ammonia as an alternative refrigerant of the Flon.

An ammonia refrigerant does not destroy the environments of the earth incontrast to the Flon, and the refrigeration effect of ammonia iscomparable to that of the Flon, and what is better, ammonia isinexpensive. However, ammonia is toxic, combustible, and insoluble in amineral oil which is used as a lubricating oil for a compressor. Inaddition, ammonia has the drawback that its discharge temperature of thecompressor is high. Accordingly, a refrigerating system which is nowutilized is constituted so as not to bring about inconveniences owing tothese drawbacks.

A typical constitution of the refrigerating system will be described inreference to FIG. 6. Reference numeral 50 is a direct expansionrefrigerating system of a single-step compression type for providingheat of -10° C. on the side of an evaporator and heat of +35° C. on theside of a condenser. The function of this refrigerating system will bemainly described. An oil-containing ammonia refrigerant which iscompressed by a refrigerant compressor 51 is treated in an oil separator52 to separate the oil therefrom, and it is then subjected to heatexchange with a cooling water 64 in a condenser 53 (taken heat: about35° C.), whereby the ammonia refrigerant is condensed/liquefied in thecondenser 53.

The oil liquefied and separated at the time of the condensation isfurther separated in an oil reservoir 55 disposed under the bottom of ahigh-pressure liquid receiver 54, and the ammonia refrigerant is thenvaporized under reduced pressure through an expansion valve 56. In anevaporator 57, heat exchange is carried out with blast load fed by a fan58 (taken heat: -10° C.), and the ammonia refrigerant is then suckedinto the compressor 51 via an ammonia oil separator 59. Afterward, thisrefrigerating cycle is repeated.

The oils stored on the bottoms of the oil separator 52, the oilreservoir 55 disposed at the bottom of the liquid receiver 54, theammonia oil separator 59 and the evaporator 57 are all collected in anoil receiver 61 via oil drawing valves 60a, 60b, 60c and 60d,respectively, and the thus collected oil is returned to the compressor51 through an oil jet portion 52a of the compressor 51 to carry outlubrication, sealing and cooling of sliding parts.

In this connection, it is well known that the refrigerating machine 50can be applied as a heat pump device by taking out heat from the side ofthe condenser 53, and therefore, they will be generically called therefrigerating machine.

As the above-mentioned lubricating oil, there is usually used a minerallubricating oil comprising of a paraffinic-based oil, a naphthenic-basedoil or the like. However, since the lubricating oil is insoluble inammonia, the oil separator is provided on the discharge side of thecompressor to separate the ammonia gas and the lubricating oildischarged from the compressor. Even if the above-mentioned separator isprovided, the lubricating oil in a mist state cannot be completelyremoved. Moreover, since the discharge side of the compressor has a hightemperature, the lubricating oil is slightly dissolved in ammonia or themist of the lubricating oil is mixed with ammonia, and the lubricatingoil gets into the refrigerating cycle together with ammonia and tends toaccumulate in pipe passages of the cycle because of being insoluble inammonia and having a larger specific gravity than ammonia. Therefore,oil drawing portions 55, 60d are must be provided at the bottom of thehigh-pressure liquid receiver 54 and on the lower inlet side of theevaporator 57, respectively, and the oil separator 59 must be alsoprovided on the gas suction side of the compressor 51. In addition, theseparated oil, after recovered in the oil receiver 61, is required toreturn to the compressor again. In consequence, the constitution isnoticeably complicate.

As described above, the lubrication oil is insoluble in the refrigerant,and therefore the oil tends to adhere to wall surfaces of heat exchangecoils in the condenser 53 and the evaporator 57, so that a heat transferefficiency deteriorates. Particularly in the evaporator having a lowtemperature, the viscosity of the oil increases and an oil drawingfluidity lowers, so that the heat transfer efficiency furtherdeteriorates.

Therefore, it is necessary to separate the insoluble oil on the inletside of the evaporator 57 as much as possible. However, if therefrigerant having a reduced pressure which has passed through theexpansion valve 56 is introduced from the upper portion of theevaporator 57, the lubricating oil cannot be prevented from getting intothe evaporator 57 owing to a difference between specific gravities, evenif a specific separator is used. For this reason, the system having theabove-mentioned constitution cannot help taking the so-called bottomfeed structure in which the inlet portion of the refrigerant is disposedon the bottom of the evaporator 57.

However, if the bottom feed structure is taken, the so-called fullliquid structure must be naturally taken in which the refrigerant can bedischarged through the upper end of the evaporator against a gravitycorresponding to the height of the evaporator 57, and as a result, alarge amount of the refrigerant is required in the refrigerating cycle.

In the case of the above-mentioned ammonia refrigerating system, its useis limited to about -20° C., but in recent years, the temperatures ofindustrial processes remarkably lower, and particularly in food fields,most of required refrigeration temperatures are -30° C. or less from theviewpoints of preventing the melting of fat at the time of thawing andkeeping qualities. Particularly in the case of an expensive food such astuna, a freezing preservation temperature is very low, in the range of-50° C. to -60° C..

Such a freezing temperature cannot be obtained by the above-mentionedsingle-step compressor, and in general, a two-step compressor is used.However, when the temperature of the evaporator is cooled to -40° C. orless by means of the above-mentioned conventional technique, thefluidity of the lubricating oil noticeably lowers as shown in Table 3given below, so that the evaporator is liable to be cloged.

In order to overcome the above-mentioned drawback, such an extremely lowtemperature ammonia two-step compression type liquid pump recyclingsystem as shown in FIG. 7 has been suggested.

The constitution of the suggested recycling system will be brieflydescribed mainly in reference to differences between this recyclingsystem and the above-mentioned conventional technique. A compressedliquid discharged from the high-pressure liquid receiver 54 to a liquidpipe 66 cools the interior of an intermediate cooler 68 by an expansionvalve 67. On the other hand, the terminal end of the liquid pipe 66 isintroduced into a supercooling pipe 69 in the intermediate cooler 68,and the compressed liquid is then cooled to about -10° C. in thesubcooling pipe 69. Afterward, the compressed liquid is vaporized underreduced pressure by an expansion valve 74 to be introduced into alow-pressure liquid receiver 70.

As a result, the refrigerant cooled to from -40° to -50° C. or less isstored in the liquid receiver 70.

This refrigerant is introduced into an evaporator 73 via a liquid pump71 and a flow rate regulating valve 72, and the refrigerant evaporatedby heat exchange (taken heat: -40° C.) with blast load fed by a fan 74in the evaporator 73 is introduced into the low-pressure liquid receiver70 to be cooled and condensed/liquefied.

On the other hand, the evaporated refrigerant in the low-pressure liquidreceiver 70 is sucked into a low step compressor 75 and compressed, andthis compressed gas is cooled in the intermediate cooler 68 and thenintroduced into the supercooling pipe 69 for heat exchange in theintermediate cooler 68 to supercool the condensed refrigerant comingthrough the above-mentioned liquid pipe 66 to about -10° C. The thussupercooled liquid is vaporized under reduced pressure by the expansionvalve 74, while introduced into the low-pressure liquid receiver 70.

The vaporized refrigerant in the intermediate cooler 68 is compressed bya high step compressor 51', and this cycle is then repeated.

Under all of the high-pressure liquid receiver 54, the intermediatecooler 68 and the low-pressure liquid receiver 70, the oil reservoirs55, 68a and 70a are disposed, respectively, and the separated oils inthese reservoirs are collected in the oil receiver 61 and then returnedagain to oil jet portions 51a, 75a on the sides of compressor 51' and75. In this connection, reference numeral 76 in the drawing is a liquidsurface float valve.

However, also in such a conventional technique, fundamental drawbackssuch as the complication of the oil recovery constitution and thedeterioration of the heat transfer efficiency cannot be overcome.Particularly on the side of the above-mentioned low-pressure liquidreceiver 70, the refrigerant cooled to from -40° to -50° C. is stored,so that the lubricating oil stored in its oil reservoir is similarlycooled to from about -40° to -50° C., so that the fluidity of thelubricating oil noticeably deteriorates. Thus, when the oil is drawn, itis necessary to temporarily raise the temperature of the oil, and as aresult, the continuous operation of the refrigeration cycle isdisturbed. In consequence, the maintenance that the above-mentionedcycle is stopped to recover the oil is necessary, each time the oil isaccumulated as much as a predetermined amount.

On the other hand, an enclosed compressor is often used in a domesticrefrigerator or air conditioner, and CFC and HCFC refrigerants such asdichlorodifluoromethane (R12) and chlorodifluoromethane (R22) have beenheretofore used. In the future, HFC containing no chlorine, for example,1,1,1,2-tetrafluoroethane (R134a) will be used, but such a Flon isexpensive. On the other hand, ammonia is more inexpensive than theabove-mentioned Flons. In addition, ammonia is excellent in the heattransfer efficiency, has a high allowable temperature (a criticaltemperature) and a high allowable pressure as the refrigerant, issoluble in water to prevent the expansion valve from plugging, and haslarge evaporation latent heat to exert a large refrigeration effect. Forthese reasons, the employment of ammonia is advantageous. However, theenclosed compressor has a structure in which an electric motor and thecompressor are integrally enclosed, and therefore ammonia itselfcorrodes copper-based materials, which makes the use of ammoniaimpossible. In addition, since ammonia is insoluble with the lubricatingoil, it is extremely difficult to recover and recycle the oil alone. Forthese reasons, ammonia cannot be used nowadays.

However, if a lubricating oil which has an excellent solubility withammonia and in which quality does not deteriorate even by a long-termuse is developed, most of the above-mentioned problems will be solved.

The lubricating oil having such a solubility has already been suggestedin the field of the Flon, and for example, an ester of a polyvalentalcohol and a polyoxy-alkylene glycol series compound are known.However, any example of the lubricating oil for the ammonia refrigeranthas not been present. Ammonia is strongly reactive, and so even when theester slightly hydrolyzes, an acid amide is formed which causes a sludgeto deposit. Moreover, these kinds of lubricating oils are poor in thesolubility with ammonia, and hence it is difficult to use theselubricating oils in combination with the ammonia refrigerant.

In view of such technical problems, an object of the present inventionis to provide a working fluid composition for a refrigerating machine(hereinafter referred to simply as "the working fluid composition")which is extremely excellent in the solubility with the ammoniarefrigerant and which can be obtained by mixing a lubricating oil havingexcellent lubricating properties and stability with an ammoniarefrigerant.

Another object of the present invention is to provide a refrigeratingmachine suitable for the above-mentioned working fluid composition. 10Still another object of the present invention is to provide a method forlubricating a refrigerating machine and a refrigerating compressormounted in the refrigerating machine by the use of the above-mentionedworking fluid composition, and according to this method, theabove-mentioned drawbacks of ammonia can be removed.

DISCLOSURE OF THE INVENTION

The present inventors have intensively researched in order to obtain theabove-mentioned working fluid composition, and they have found that anether compound having a specific structure in which all of the terminalOH groups of a polyoxyalkylene glycol are replaced with OR groups(hereinafter referred to simply as "the polyether") is excellent insolubility with ammonia, and that the ether compound can exert excellentlubricating properties and stability even in the presence of ammonia. Inconsequence, the present invention has now been completed.

That is, the first aspect of the present invention is directed to aworking fluid composition which comprises a mixture of ammonia and alubricating oil for an ammonia refrigerating compressor containing, as abase oil of the lubricating oil, a compound represented by the formula(I)

    R.sub.1 -- --O--(PO).sub.m --(EO).sub.n --R.sub.2 !.sub.x  (I)

wherein R₁ is a hydrocarbon group having 1 to 6 carbon atoms, R₂ is analkyl group having 1 to 6 carbon atoms, PO is an oxypropylene group, EOis an oxyethylene group, x is an integer of from 1 to 4, is a positiveinteger, and n is 0 or a positive integer.

The second aspect of the present invention is directed to arefrigeration cycle or a heat pump cycle which is constituted by puttingan ammonia refrigerant and a lubricating oil into a refrigeratingmachine, a ratio of the lubricating oil to the ammonia refrigerant being2% by weight or more, the lubricating oil being soluble in the ammoniarefrigerant and being free from phase separation even at an evaporationtemperature of the refrigerant.

In this case, the ammonia refrigerant and the lubricating oil may bepreviously mixed to form the working fluid composition, or they may beseparately put into the refrigeration cycle or the heat pump cycle andthe working fluid composition may be formed in the cycle.

Furthermore, the lubricating oil which can be used in the presentinvention is not limited to the lubricating oil defined in the firstaspect of the present invention, and any lubricating oil is acceptable,so long as it is easily soluble in the ammonia refrigerant and does notbring about the phase separation even at the evaporation temperature ofthe refrigerant.

A preferable ammonia refrigerating machine using an enclosed ammoniacompressor directly connected to an electric motor can be provided bydisposing a stator core around a rotor so as to surround the rotor viaairtight diaphragms and so as to surround the rotor via a predeterminedspace, and disposing an introducing portion through which theabove-mentioned composition can be introduced between a space of theabove-mentioned rotor and the compressor.

Furthermore, the lubricating oil in which the compound of the formula(I) is employed as the base oil is not always used only as the workingfluid in which the lubricating oil is dissolved in ammonia, but it canalso be used singly as a lubricating oil for the ammonia compressor.This is the third aspect of the present invention.

Next, the above-mentioned aspects of the present invention will bedescribed in detail.

In the first place, the compound represented by the formula (I) is apolyether which is a polymer of propylene oxide, or a polyether which isa random copolymer or a block copolymer of propylene oxide and ethyleneoxide.

The compound of the formula (I) is the so-called polyoxyalkylene glycolcompound, and there are known many examples in which this compound isused as the lubricating oil for a refrigerating machine using HCFC orCFC as the refrigerant. For example, U.S. Pat. No. 4,948,525 (whichcorresponds to Japanese Patent Application Laid-open Nos. 43290/1990 and84491/1990) suggests a polyoxyalkylene glycol monoether having thestructure of R₁ --(OR₂)_(a) --OH (wherein R₁ is an alkyl group having 1to 18 carbon atoms, and R₂ is an alkylene group having 1 to 4 carbonatoms); U.S. Pat. No. 4,267,064 (which corresponds to Japanese PatentPublication No. 52880/1986) and U.S. Pat. No. 4,248,726 (whichcorresponds to Japanese Patent Publication No. 42119/1982) suggest apolyglycol having R₁ --O--(R₂ O)_(m) --R₃ (wherein each of R₁ and R₃ ishydrogen, a hydrocarbon group or an aryl group); U.S. Pat. No. 4,755,316(which corresponds to Japanese Patent Disclosed Publication No.502385/1990) suggests a polyalkylene glycol having at least two hydroxylgroups; U.S. Pat. No. 4,851,144 (which corresponds to Japanese PatentApplication Laid-open No. 276890/1990) suggests a combination of apolyether polyol and an ester; and U.S. Pat. No. 4,971,712 (whichcorresponds to Japanese Patent Application Laid-open No. 103497/1991)suggests a polyoxyalkylene glycol having one hydroxyl group obtained bycopolymerizing EO and PO. In all of these publications, it is describedthat the solubility of these lubricating oils in HFC and HCFC isexcellent.

On the other hand, the present applicant has filed Japanese PatentApplication Laid-open Nos. 259093/1989, 259094/1989, 259095/1989 and109492/1991 regarding polyoxyalkylene glycol monoethers andpolyoxyalkylene glycol diethers having structures of R₁ --O--(AO)_(n)--H and R₁ --O--(AO)_(n) --R₂ as the lubricating oils of the compressorsfor HFC.

However, these known publications do not refer to any relation withammonia. In view of the fact that HFC and HCFC are inactive, the factthat ammonia is largely reactive, and the fact that both of them arequite different from each other in solubility, the above-mentionedpieces of the information are not useful for the completion of thepresent invention using the ammonia refrigerant.

With regard to the ammonia refrigerant, it is described in "SyntheticLubricant and Their Refrigeration Applications", LubricationEngineering, Vol. 46, No. 4, p. 239-249 that poly-α-olefin andisoparaffinic mineral oils having high viscosity indexes are useful asthe lubricating oils for the ammonia refrigerant, and an ester producesa sludge and solidifies by a long-term use. In addition, U.S. Pat. No.4,474,019 (which corresponds to Japanese Patent Application Laid-openNo. 106370/1983) suggests the improvement of a refrigerating systemusing an ammonia refrigerant. However, also in these known publications,there is not described any relation between the ammonia refrigerant andthe polyether compound.

The polyether of the formula (I) has a viscosity necessary as thelubricating oil, and in compliance with its use, it can have a viscosityof 22-68 cSt at 40° C. or 5-15 cSt at 100° C. A factor which has a largeinfluence on this viscosity is molecular weight, and the molecularweight necessary to attain the above-mentioned viscosity is preferablyin the range of 300 to 1800.

The polyether of the formula (I) is an polyether in which all of theterminals are sealed with R₁ and R₂. Here, R₁ is a hydrocarbon grouphaving 1 to 6 carbon atoms, and this hydrocarbon group means thefollowing (i) or (ii). That is, R₁ is (i) a saturated straight-chain orbranched hydrocarbon group having 1 to 6 carbon atoms, typically analkyl group having 1 to 6 carbon atoms derived from an aliphaticmonovalent alcohol having 1 to 6 carbon atoms, that is, any one of amethyl group, an ethyl group, a propyl group, an isopropyl group, abutyl group, an isobutyl group, a pentyl group, an isopentyl group, ahexyl group and an isohexyl group. In particular, R₁ is preferably analkyl group having 1 to 4 carbon atoms, more preferably an alkyl grouphaving 1 to 2 carbon atoms, that is, a methyl group or an ethyl group.And, R₁ is (ii) a hydrocarbon residue derived from a divalent to atetravalent saturated aliphatic polyvalent alcohol, typically ethyleneglycol, propylene glycol, diethylene glycol, 1,3-propanediol,1,2-butanediol, 1,6-hexanediol, 2-ethyl-1,3-hexanediol, neopentylglycol, trimethylolethane, trimethylolpropane, triemthylolbutane orpentaerythritol, that is, a hydrocarbon group in which all the hydrogenatoms of 1 to 2 hydroxyl groups in the divalent to the tetravalentalcohol are substituted. Therefore, x of the formula (I) is an integerof from 1 to 4 corresponding to the valence of the alcohol which is thesource compound of the hydrocarbon group of the above-mentioned R₁. Inorder to particularly increase the solubility of the lubricating oil inammonia, it is preferred that x is 1 and R₁ is a methyl group or anethyl group.

Furthermore, R₂ is an alkyl group having 1 to 6 carbon atoms. If thealkyl group having 7 or more carbon atoms is used, the phasic separativetemperature of the lubricating oil and ammonia is caused rises, so thatthe objects of the present invention cannot be achieved. If R₂ is thealkyl group having 1 to 4 carbon atoms, moreover, 1 to 2 carbon atoms,the solubility of the lubricating oil with ammonia increases, that is,the phasic separative temperature further lowers preferably. If x isfrom 2 to 4, R₂ are 2 to 4 alkyl groups. These alkyl groups may be sameor different, and in order to maintain the preferable solubility, R₂ ispreferably the alkyl group having 1 to 4 carbon atoms, particularlypreferably 1 to 2 carbon atoms.

Generally speaking, as the number of the carbon atoms in R₁ and R₂increases, the phase separation temperature of the lubricating oil andammonia tends to increase. Therefore, in order to maintain the goodsolubility, the total number of the carbon atoms of R₁ and R₂ ispreferably 10 or less, more preferably 6 or less, further preferably 4or less, most preferably is 2. In the case that one or both of R₁ and R₂are hydrogen, the lubricating oil reacts with ammonia to form a sludge,with the result that the object of the present invention cannot beachieved.

If only a portion of the hydroxyl groups of the monovalent to thetetravalent alcohol remains unreacted in the synthesis of the compoundof the formula (I), the obtained polyether will unpreferably form thesludge during a use for a long time. Therefore, it is preferable thatthe remaining hydroxyl groups of the alcohol are as little as possible,and typically, a hydroxyl value of the compound having the formula (I)is 10 mg KOH/g or less, preferably 5 mg KOH/g or less.

As described above, the viscosity of the lubricating oil in which thepolyether compound represented by the formula (I) is used as the baseoil is in the range of from 22 to 68 cSt at 40° C., or from 5 to 16 cStat 100° C. This viscosity is necessary to maintain good lubricatingproperties under the coexistence with ammonia. In order to maintain thegood solubility of the lubricating oil in ammonia, the average molecularweight of the lubricating oil is preferably in the range of from 300 to1800. If the average molecular weight of the lubricating oil is lessthan 300, the viscosity is low, so that the good lubricating propertiescannot be obtained. On the other hand, it is more than 1,800, thesolubility with ammonia is poor. The control of the average molecularweight can be achieved by suitably selecting R₁ and R₂, andpolymerization degrees m and n.

Furthermore, a relative ratio between the polymerization degree (m) ofthe oxypropylene group and the polymerization degree (n) of theoxyethylene group, i.e., a value of m/(m+n), is important for thelubricating properties, a low-temperature fluidity and the solubilitywith ammonia. That is, n is too large with respect to m, a pour point ishigh and the solubility with ammonia deteriorates. In view of thisviewpoint, the value of m/(m+n) is preferably 0.5 or more. A compound ofthe formula (I) in which n is 0 is excellent in the solubility withammonia and the lubricating properties. However, a polyether which is acopolymer of oxypropylene (PO) and oxyethylene (EO) and which m/(m+n) is0.5 or more maintains the better solubility and has the more improvedlubricating properties than a monopolymer of oxypropylene (PO). On theother hand, a polyether obtained by polymerizing oxyethylene alone orpolymerizing oxyethylene and oxypropylene in a larger amount ofoxyethylene has the high pour point and a high hygroscopicity, andtherefore care should be taken to avoid such results. On the viewpointsof the solubility with ammonia, the lubricating properties and thefluidity, the value of m/(m+n) is preferably in the range of from 0.5 to1.0, more preferably from 0.5 to 0.9, most preferably from 0.7 to 0.9.

Furthermore, as the copolymer of oxyethylene and oxypropylene, a blockcopolymer is shown in the formula (I) for convenience, but in practice,a random copolymer and an alternating copolymer are also acceptable inaddition to the block copolymer. In the block copolymer, the bondingorder of the oxyethylene portion and the oxypropylene portion is notrestrictive, and in other words, either of the oxyethylene portion andthe oxypropylene portion may be bonded to R₁. However, a polyethercompound obtained by polymerizing an oxyalkylene having 4 or more carbonatoms such as oxybutylene is not preferable, because of being solublewith ammonia.

Next, the determination of the solubility with the ammonia refrigerant,i.e., the phase separation temperature, is made in compliance with a useto be selected. For example, in the case of an extremely low temperaturerefrigerating machine, the lubricating oil having a phase separationtemperature of -50° C. or less is necessary. In the case of a usualrefrigerator, the lubricating oil having that of -30° C. or less isused, and in the case of an air conditioner, the lubricating oil havingthat of -20° C. or less is usable.

Particularly when the lubricating oil having the low phase separationtemperature is necessary, R₁ is most preferably a methyl group.

The compounds of the formula (I) may be used singly or in a combinationof two or more thereof. For example, a polyoxypropylene dimethyl etherhaving a molecular weight of 800-1000 and a polyoxyethylene propylenediethyl ether having a molecular weight of 1200-1300 may be used singlyor in the form of a mixture thereof in a ratio of 10:90 to 90:10 (byweight), and in this case, the viscosity of the mixture at 40° C. is inthe range of from 32 to 50 cSt.

The polyether compound of the formula (I) can be obtained bypolymerizing a monovalent to tetravalent alcohol having 1 to 6 carbonatoms or its alkaline metal salt as a starting material with an alkyleneoxide having 2 to 3 carbon atoms to prepare an ether compound in whichone terminal of the chain polyalkylene group is combined with thehydrocarbon group of the material alcohol by an ether bond and the otherterminal of the polyalkylene group is a hydroxyl group, and thenetherifying this hydroxyl group.

In order to etherify the hydroxyl group at the terminal of the ethercompound, there are a method in which this ether compound is firstreacted with an alkaline metal such as metal sodium or an alkaline metalsalt of a lower alcohol such as sodium methylate to form an alkalinemetal salt of the ether compound, and this alkaline metal salt is thenreacted with an alkyl halide having 1 to 6 carbon atoms; and a method inwhich the hydroxyl group of the ether compound is converted into ahalide, and the compound is then reacted with a monovalent alcoholhaving 1 to 6 carbon atoms.

Therefore, it is not always necessary to use the alcohol as the startingmaterial, and a polyoxyalkylene glycol having hydroxyl groups at bothterminals can also be used as the starting material. In any case, thepolyether compound of the formula (I) can be prepared in a knownsuitable method.

The refrigerating machine oil of the present invention stably dissolvesin ammonia in an extremely wide mixing ratio, and can exert goodlubricating properties in the presence of ammonia.

As described below, the mixing ratio of the lubricating oil can belowered by adding an additive such as diamond cluster, while theabove-mentioned lubricating properties are kept up.

Therefore, the refrigerating machine oil of the present inventioncontains the compound represented by the formula (I) as the base oil,and the working fluid composition which is circulated through therefrigeration cycle or the heat pump cycle of the present inventionpreferably comprises ammonia and the polyether compound of the formula(I) in a ratio of 98:2 (by weight) or more.

To the lubricating oil and the working fluid composition for therefrigerating machine of the present invention, various kinds ofadditives can be added, if necessary. Examples of the additives includean etreme-ressure reagant such as tricresyl phosphate, an amine-basedantioxidant, a benzotriazole-based metallic inactivating agent and ananti-foaming agent of silicone or the like. In this case, those which donot react with ammonia to form a solid should be selected. Therefore, aphenolic antioxidant cannot be used. Furthermore, a lubricating oilwhich has a possibility of reacting with ammonia, for example, a polyolester should not be added, and a mineral oil-based lubricating oil whichis insoluble in ammonia should not be mixed.

Next, reference will be made to the second aspect of the presentinvention in which the above-mentioned working fluid composition isused. In this aspect of the 10 present invention, an ammonia refrigerantand a lubricating oil which is soluble in the ammonia refrigerant andwhich does not bring about the phase separation at the evaporationtemperature of the refrigerant are put into a refrigerating machine soas to form a refrigeration cycle or a heat pump cycle, and the ratio ofthe lubricating oil to the ammonia refrigerant is 2% by weight or more.

The ratio between ammonia and the lubricating oil depends upon the kindof compressor, but fundamentally, it is preferable to decrease theamount of the lubricating oil as much as possible for the sake ofimproving a heat transfer efficiency, so long as a lubricatingperformance is maintained.

For example, in the refrigerating machine using a rotary compressor ofthe present invention, even if the blend weight ratio of the ammoniarefrigerant and the lubricating oil is set to about 70-97:30-3,sufficient lubricating properties and a refrigerating capacity can beobtained, and the undermentioned performances can be remarkablyimproved.

That is, if 3% or more of the oil is dissolved in ammonia, the dissolvedoil is liable to get into sliding portions of the compressor, whereby ascratch can be decreased and the refrigerating cycle constitution can beextremely simplified.

In addition, when ultrafine diamond having an average particle diameterof 150 Å or less, preferably 50 Å or less or ultrafine diamond coveredwith graphite is added to the lubricating oil constituting the workingfluid composition, the blend ratio of the lubricating oil can be loweredto about 2% without any problem.

As such diamond, there is preferably used cluster diamond obtained byexploding an explosive substance in an explosion chamber filled with aninert gas to synthesize ultrafine diamond, and then purifying the same,or carbon cluster diamond obtained by covering the cluster diamond withgraphite, for example, as described in New Diamond, "Characteristics ofUltrafine Diamond Powder by New Explosion Method and its Application",Vol. 8, No. 1, 1991. When 2-3% by weight of this kind of diamond isadded to the lubricating oil, the blend ratio of the lubricating oil inthe working fluid can be lowered to 2% by weight.

Furthermore, the above-mentioned lubricating oil does not give rise tothe phase separation even at the evaporation temperature of therefrigerant and is excellent in low temperature fluidity, and hencethere is not the fear that the separated oil adheres to heat exchangecoils not only on the condenser side but also on the evaporator side. Inconsequence, the heat transfer efficiency can largely improved and it isnot necessary to dispose the oil recovery mechanism and the oilseparator in the above-mentioned refrigerating cycle, whereby a circuitconstitution can also be largely simplified.

In the compressor, the lubricating oil is dissolved in the refrigerantand gets into the sliding portions, which is useful to further preventthe scratch.

In this case, another constitution may be made so that the working fluidobtained by mixing the ammonia refrigerant and the lubricating oil whichhas been compressed by the above-mentioned compressor may be circulatedthrough the refrigerating cycle and the heat pump cycle withoutinterposing the oil recovery device.

In this case, even if the blend ratio of the lubricating oil is 10% byweight or more, a certain amount of the lubricating oil is stored in thecompressor, and therefore the blend ratio of the lubricating oil in therefrigerating cycle, particularly the blend ratio of the lubricating oilin the working fluid composition in the evaporator can be set to 7% orless, whereby a more preferable heat transfer efficiency can beobtained.

Still another constitution may be made so that a part of the lubricatingoil in the working fluid composition which has been compressed by thecompressor can be returned to the compressor. Particularly in the lattercase, the blend ratio of the lubricating oil can be easily increased onthe side of the compressor, and the blend ratio of the lubricating oilwhich is introduced into the circulating cycle, particularly the side ofthe evaporator can be easily decreased as much as possible.

Needless to say, the present invention is applicable not only to thesingle-step compression type refrigerating machine but also to thetwo-step compressor type refrigerating machine.

The above-mentioned composition has excellent lubricating properties andsolubility even the evaporation temperature or less of the refrigerant,and therefore a top feed structure can be taken in which the compositionpassed through the expansion valve or the intermediate cooler isintroduced into the evaporator through its top side, whereby it isunnecessary to employ the so-called liquid full structure. Inconsequence, the amount of the refrigerant (composition) to becirculated can be reduced and the high refrigerating effect can beobtained.

Furthermore, the composition is soluble with the lubricating oil even atthe evaporation temperature or less of the refrigerant, but there is thefear that the composition is separated under severe conditions of thelow-temperature vaporization in the compressor. In addition, if theevaporator has the top feed constitution, the separated oil is directlyintroduced into the compressor to cause problems of knocking and thelike.

Thus, it is preferable to dispose an oil reservoir for temporarilystoring the separated oil, for example, as the double riser, in themiddle of an introductive pipe passage connecting the evaporator to thecompressor and a remixing portion for remixing the lubricating oil inthe oil reservoir with the working fluid composition to be introducedinto the compressor in the pipe passage.

The employment of the above-mentioned constitution can solve the problemregarding the insolubility of the lubricating oil in ammonia as therefrigerant.

The problems regarding the strong corrosive properties and theelectrical conductivity of ammonia are not solved yet, and inparticular, the problem of the corrosive properties to a copper materialstill remains. If this problem is not solved, it is difficult to applyammonia to an enclosed compressor, particularly a domestic refrigerator.

Thus, the present invention provides an ammonia refrigerating machineusing an enclosed ammonia compressor in which an electric motor isdirectly connected to the ammonia refrigerant compressor, said ammoniarefrigerating machine being characterized by disposing a stator corearound a rotor on the side of the electric motor via an airtight sealingportion formed on the side surface of the stator core so as to surroundthe rotor via a predetermined space, and disposing an introducingportion through which the above-mentioned composition can be introducedbetween a space in the above-mentioned rotor and the compressor.

According to the present invention, the side of the rotor provided withwindings is isolated from a rotor receiving space into which the ammoniarefrigerant and the like flow, by the airtight sealing portion, andtherefore the windings and the like are not attacked. In addition, thecomposition containing the lubricating oil flows through the rotorreceiving space side, so that the lubrication of bearings of therotating shaft of the rotor and the like is not impaired and thepressure of the fluid composition in both the spaces can be uniformed.

In this case, the above-mentioned airtight sealing portion may beconstituted by cylindrical can for surrounding the rotor, but in thecase that the can is used, an alternating magnetic flux by theexcitation of a rotor coil becomes a revolving flux and penetrates thecan in the above-mentioned space to revolve the rotor. However, eddycurrent flows in the can to generate an eddy-current loss, whichoccupies about half of a motor loss, heats the motor and deterioratesits efficiency.

Thus, the stator core can be constituted as a pressure-resistantenclosed structure container. Furthermore, an insulating thin film canbe formed on the inner periphery of the stator core, or a seal membercan be arranged on the front surface of the stator core which confrontsthe rotor in which the windings of the stator core have been insertedinto open grooves, and the open grooves may be constituted via the sealmember so as to be capable of airtightly sealing.

In consequence, the above-mentioned drawbacks of the can are solved, andsince the stator core itself functions as a pressure-resistantcontainer, the can is unnecessary. In addition, the stator core is madeof thick field cores, and hence sufficient pressure-resistant strengthcan be given.

When a constitution is made so that the composition can leak through atransmission shaft portion for transmitting the revolution of the rotorto the compressor side, the electric motor side can be easily lubricatedand its constitution is easy, because the sealing is incomplete.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a direct expansion refrigeratingmachine of a single-step compression type regarding an embodiment of thepresent invention.

FIG. 1A is a detail of FIG. 1, as shown.

FIG. 2 is a schematic view showing an extremely low refrigeratingmachine of a two-step compression type regarding an embodiment of thepresent invention.

FIG. 3 is a schematic view showing a direct expansion refrigeratingmachine of a single-step compression type regarding another embodimentof the present invention.

FIG. 4 is a vertical section of an enclosed compressor directlyconnected to an electric motor regarding an embodiment of the presentinvention.

FIG. 5 is an enlarged view of the main portion showing a sectionalstructure of a stator in FIG. 4.

FIG. 5(A) is a detail of FIG. 5, as shown.

FIG. 5(B) is an alternative embodiment of the detail shown in FIG. 5(A).

FIG. 6 is a schematic view showing a direct expansion refrigeratingmachine of a single-step compression type regarding a conventionaltechnique.

FIG. 7 is a schematic view showing an extremely low refrigeratingmachine of a two-step compression type regarding a conventionaltechnique.

BEST MODE FOR CARRYING OUT THE INVENTION

In the first place, as a lubricating oil, there were used polyethercompounds (Examples 1 to 8) shown in Table 1, a naphthenic mineralrefrigerating oil (Comparative Example 1), a branched alkylbenzene(Comparative Example 2) and (poly)ether compounds (Comparative Examples3 to 8) shown in Table 2, and evaluation was made by measuringsolubility with ammonia, falex seizure load, color total acid numbersand the change of appearance of samples before and after bomb testsunder an ammonia atmosphere.

In this connection, physical properties of the naphthenic mineralrefrigerating oil in Comparative Example 1 and the branched alkylbenzenein Comparative Example 2 in Table 2 were as follows:

    ______________________________________                                                    Naphthenic Mineral                                                            Refrigerating                                                                            Branched                                                           Oil        Alkylbenzene                                           ______________________________________                                        Density       0.888        0.870                                              Kinematic Viscosity                                                                         4.96         4.35                                               cSt (100° C.)                                                          Flash Point (°C.)                                                                    180          178                                                ______________________________________                                    

Furthermore, the procedures of each test used in the evaluation ofcompositions of the present invention were as follows:

Average molecular weight: average molecular weight was measured by GPC(gel penetration chromatography).

Kinematic viscosity: This was measured in accordance with JIS K 2283.

Solubility with ammonia: 5 g of a sample oil and 1 g of ammonia wereplaced in a glass tube, and then cooled at a rate of 1° C. per minutefrom room temperature, whereby a temperature at which the phaseseparation occurred was measured.

Falex seizure load: This was measured in accordance with ASTM D-3233-73.

Bomb test: 50 g of a sample oil was poured in a 300 ml bomb in which 3 mof an iron wire having a diameter of 1.6 mm was placed as a catalyst,and the bomb was pressurized up to 0.6 kg/cm² G with ammonia and furtherpressurized up to 5.7 kg/cm² G with a nitrogen gas. Afterward, thesample was heated up to 150° C. and then maintained at this temperaturefor 7 days. After it was cooled to room temperature, ammonia was removedfrom the sample oil under vacuum condition. In this case, color andtotal acid number of the sample were measured before and after the test.The stability of the sample under the ammonia atmosphere was evaluatedby the change of its appearance. In this connection, the evaluation ofthe appearance was graded as follows:

No change: In the case that the appearance did not change before andafter the test.

Solidification: In the case that the sample solidified after the test.

The results of the test are set forth in Tables 1 and 2.

It is apparent from the results in Tables 1 and 2 that the polyethercompounds in Examples 1 to 8 are excellent in solubility with ammonia,lubricating properties and stability under the ammonia atmosphere. Themixtures of these polyether compounds and ammonia can exert theirfunctions, when put into an ammonia compressor and then used. As aresult, the ammonia compressor can take a compact and maintenance-freeconstitution, and therefore the applications of the ammonia compressorcan be effectively increased.

However, the naphthenic mineral refrigerating oil, the branchedalkylbenzene and the (poly)ethers in Comparative Examples 3 to 8 shownin Table 2 are insoluble at room temperature or have the solubility at alow temperature of -50° C., but they solidify in the bomb tests. As aresult, these oils cannot be used in a refrigerating cycle in whichcompression, condensation and expansion are repeated.

Next, reference will be made to the refrigerating system using a workingfluid composition in which a lubricating oil and an ammonia refrigerantare mixed.

FIG. 1 shows a direct expansion refrigerating machine of a single-stepcompression type regarding the embodiment of the present invention, anda refrigerating cycle is fed with R-717 (the ammonia refrigerant) as therefrigerant and the polyether in Example 1 as the lubricating oil in aratio of 90 parts by weight:10 parts by weight.

In this drawing, reference numeral 11 is a refrigerant compressor, andthe refrigerant working fluid formed by mutually dissolving the ammoniarefrigerant compressed in the refrigerant compressor 11 and thelubricating oil is directly led to a condenser 12 without passingthrough an oil separator, and then condensed/liquefied by heat exchange(taken heat: 30° C. or so) with cooling water in the condenser 12.

The thus condensed working fluid is stored in a high-pressure liquidreceiver 14, evaporated under reduced pressure by means of an expansionvalve 13, introduced into an evaporator 15 through an inlet 15a providedat the upper end of the evaporator 15 in accordance with top feed,heat-exchanged with blast load fed by a fan 16 (taken heat: -15° to -20°C. or so), and then sucked on the gas suction side of the compressor 11via a double riser 17. Afterward, the above-mentioned refrigeratingcycle is repeated.

Here, the double riser 17, as already known, has a main pipe passage 171having a U-shaped local oil reservoir 172 on the outer side of an outlet15b of the evaporator 15 and a by-pass pipe passage 173 for by-passingthe main pipe passage. Thus, the oil slightly separated by evaporationin the evaporator 15 is stored in the oil reservoir 172 andsimultaneously led to a low-pressure sucking pipe 19 via the main pipepassage 171. The by-pass pipe passage 173 is constituted in the form ofa thin pipe to give a chock resistance. Thus, when the main pipe passage171 is clogged by the oil reservoir, the clogging oil is led to thelow-pressure sucking pipe 19 by the flow rate of the evaporatedrefrigerant containing the lubrication oil which flows through theby-pass pipe passage 173, so that they are mixed and dissolved again,and then led to the suction side of the compressor 11.

Therefore, according to this embodiment, an oil separator and the likeare unnecessary, and it is also unnecessary to provide any oil reservoiron the bottom of the liquid receiver as in the case of a conventionaltechnique shown in FIG. 6. Furthermore, the local oil reservoir 172 isprovided in the double riser 17, whereby the mixing and solution arecarried out again and the mixture is introduced into the compressor 11.Thus, an oil recovery mechanism and a return circuit for returning tothe side of the compressor 11 again are unnecessary, whereby the cycleconstitution can be extremely simplified.

In the present embodiment, the refrigerant is soluble with thelubricating oil even at an evaporation temperature or less, andtherefore the top feed can be taken in which the refrigerant having areduced pressure passed through the expansion valve 13 is introducedinto the evaporator 15 through the upper portion of the evaporator 15.In consequence, the refrigerant can pass through the evaporator bygravity, and it is unnecessary to take the so-called liquid fullstructure. According to experiments of the present inventors, even ifthe amount of the refrigerant was decreased as much as 10% or more ascompared with the conventional example shown in FIG. 6, a higherrefrigerating effect than the above-mentioned conventional example couldbe obtained.

In the present embodiment, even if the ammonia refrigerant and thelubricating oil are fed in a ratio of 90 parts by weight:10 parts byweight, a certain amount of the lubricating oil is stored in thecompressor 11 and therefore the weight ratio of the working fluidcomposition which circulates through the refrigerating cycle is lowerthan the above-mentioned feed weight ratio. In particular, a blend ratiocirculating through the evaporator is 5% or less, and therefore the heattransfer efficiency on the evaporation side can be further improved.

In this connection, the above-mentioned compressor is suitable for avariable blade type rotary compressor or a reciprocating compressor.

In the present embodiment, operation is carried out at an evaporationtemperature of from -15° to -20° C. at a higher compression ratio thanthe above-mentioned conventional technique, but even if such aconstitution is taken, the working fluid does not deteriorate andsludging does not occur, so that a high reliability can be kept up for along period of time.

Furthermore, the lubricating oil does not adhere to the wall surfaces ofheat exchange coils in the condenser 12 and the evaporator 15, and theheat transfer efficiency is improved as much as 60% or more as comparedwith the conventional example shown in FIG. 6 in which the naphthenicmineral refrigerating oil is used.

Moreover, since the ammonia and the lubricating oil which constitute theabove-mentioned working fluid have a power to dissolve in water, adehumidifying agent such as silica gel and a dehumidifying mechanism donot have to be provided as in a Flon refrigerating cycle.

In the above-mentioned working fluid, it is necessary to increase theratio of the refrigerant in a range in which the lubricating propertiesof the compressor 11 do not decline, but if the amount of thelubricating oil is lowered to 5% by weight or less, a lubricating poweractually deteriorates.

In such a case, 2 to 3% by weight of cluster diamond or carbon clusterdiamond obtained by covering the cluster diamond with graphite which hasan average particle diameter of about 50 Å or less can be added to thelubricating oil to further lower the blend ratio of the lubricating oilin the above-mentioned working fluid.

In addition, as shown in FIG. 3, the liquid refrigerant passed throughthe condenser 14 is utilized to heat the working fluid compositioncontaining the oil slightly separated by evaporation in the evaporator15 by a heat exchanger 150, whereby the separated oil is dissolved inthe composition again. In consequence, the double riser 17 is alsounnecessary.

In order to improve the lubricating properties, the blend ratio of thelubricating oil of the working fluid composition may be increased, andan oil separator 25 and a return circuit 26 for returning the oilseparated in the separator 25 to the compressor 11 again may be providedon the outlet side of the compressor.

Particularly, in the case of an oil cooling type screw compressor, theoil separator 25 and the return circuit 26 for returning the oilseparated in the separator 25 to the compressor side again is preferablyprovided on the outlet side of the compressor 11.

In this case, even if the ammonia refrigerant and the lubricating oilare fed in a ratio of 90-80 parts by weight:10-20 parts by weight, theblend ratio of the lubricating oil in the closed cycle of the compressor11/the oil separator 25/the return circuit 26 can be increased, and theblend ratio of the lubricating oil in another refrigerating cycle can beset to an extremely low level. For example, the ratio of the lubricatingoil on the side of the compressor 11 can be set to 90% or more, and theblend ratio of the lubricating oil on the side of the evaporator 15 canbe set to 3% or less, further 0.5% or so.

As shown in Examples 4, 6, 7 and 8 in the above-mentioned table, whenthe working fluid is prepared by using the lubricating oil whose phaseseparation temperature is -50° C. or less, the extremely lowrefrigerating machine can be simply constituted without taking a liquidpump recycling system structure.

This constitution will be briefly described in reference to FIG. 2. FIG.2 shows an extremely low temperature refrigerating system in which R-717(an ammonia refrigerant) as the refrigerant and a polyether in Example 6as the lubricating oil are fed to the refrigerating cycle in a ratio of95 parts by weight:5 parts by weight. Reference numeral 21 is a low-stepcompressor. The compressed working fluid in which the ammoniarefrigerant and the lubricating oil are mutually dissolved is cooled toabout -10° C. in an intermediate cooler 22, and then led to a high-stepcompressor 11.

The refrigerant working fluid compressed in the high-step compressor 11is directly led to a condenser 12, and the working fluid is thencondensed/liquefied in the condenser 12 by heat exchange (taken heat:35° C. or so) with cooling water (a cooling water pipe 18).

The thus condensed working fluid is stored in a high-pressure liquidreceiver 14, and then vaporized under reduced pressure by an expansionvalve 20 to cool the intermediate cooler 22 to about -10° C. Next, theworking fluid liquefied by the cooling is introduced into an evaporator15 through an inlet 15a disposed on the top of the evaporator 15,heat-exchanged with blast load fed by a fan 16 (taken heat: -15° C.),and then sucked on the gas suction side of the compressor 21 via adouble riser 17. Afterward, the above-mentioned refrigerating cycle isrepeated.

Therefore, also in this embodiment, an oil reservoir and an oil recoverymechanism are unnecessary in the high-pressure liquid receiver 14 andthe intermediate cooler 22, and in contrast to a conventional techniqueshown in FIG. 7, a liquid pump recycling mechanism for recycling therefrigerant liquid between a low-pressure liquid receiver and theevaporator is unnecessary, so that the refrigerating cyclingconstitution can be remarkably simplified.

As shown in Table 3, the working fluid composition used in thisembodiment is well soluble with the refrigerant even at -50° C. at whichfluidity is an evaporation temperature or less, and fluidity is alsogood, about 4.5 seconds. Therefore, the top feed can be taken. Even ifthe amount of the refrigerant is decreased, a higher refrigeratingeffect can be obtained than the conventional example having a bottomfeed structure. In addition, a heat transfer efficiency at an extremelylow temperature in the evaporator can also be improved.

Furthermore, the handling of the oil is sufficient only by providing alocal oil reservoir such as the double riser arranged on the outlet sideof the evaporator 15 and a remixing/dissolving structure. Thus, therefrigerating cycle can be continuously driven for a long period of timewithout temporarily stopping the cycle for the oil drawing, wherebyoperators and maintenance can be easily omitted.

By employing the above-mentioned constitution, the problem based on theinsolubility of oil in the refrigerant can be solved.

However, the problems regarding the strong corrosive properties and theelectrical conductivity of ammonia are not solved yet, and inparticular, the problem of the corrosive properties to an electricalcopper wire still remains. If this problem is not solved, it isdifficult to apply ammonia to an enclosed compressor, particularly adomestic refrigerator.

A first solution is to apply a canned motor.

That is, in the enclosed motor directly connected to a fluid machineusing the ammonia refrigerant, the employment of a can type motor isinvestigated in which a cylindrical can is inserted and fix between astator and a rotor to prevent the ammonia refrigerant from leaking tothe stator arranged on the outer periphery of the can.

However, in the can, a high-density alternating magnetic fluxinterlinks, and an eddy-current loss and a magnetic resistance in aspace inclusive of the can increase. In addition, a large amount of heatis generated owing to excitation loss and the like, so that theefficiency of the canned motor deteriorates.

Thus, if the stator is separated from the rotor and the side of thestator is sealed to prevent the leakage of ammonia without using thecan, any particular problem is not present.

FIGS. 4 and 5 are concerned with an embodiment of such a constitution,and they show the constitution of an enclosed compressor in which amotor is directly connected to a screw compressor. In the first place,the constitution on the side of a screw compressor A will be described.Reference numeral 31 is a sucking orifice for introducing theabove-mentioned soluble working fluid which will be compressed, asindicated by an arrow; numeral 32 is an outlet for discharging therefrigerant gas compressed by a screw rotor 30 to the side of thecondenser; 33 is a rotor housing for covering them; 34A is a bearinginserted into a disc bearing housing 35 and supports a rotor shaft 37ainto which a rotating shaft 36 is inserted via a sprocket shaft.Moreover, a rotor shaft 37b on the other side is supported by a bearing34B.

In this case, an incomplete sealing state is established between therotor shaft 37a and the bearing 34A so that the working fluidcomposition may be introduced from the compressor A side to the motor Bside. Furthermore, a return hole 39 of the working fluid which hasflowed to the motor B side is provided under the disc bearing housing 35to uniform the pressure of the space in the rotor 41 on the compressor Aside and the motor side.

On the other hand, the motor B side is equipped with a rotor 41 fixed bythe above-mentioned rotating shaft 36 and a stator 42 surrounding therotor 41. As shown in FIG. 5, the stator 42 is composed of stator core43 comprising many laminated field core plates 43a and windings 45received in U-shaped open grooves 44 extending in an axial direction.Reference numeral 45a is a prolonged coil of each of the windings whichare arranged on both the sides in the axial direction.

The above-mentioned stator core 43 is formed by applying an insulatingresin coating material or another additive 46 onto the surfaces of themany laminated field core plates 43a and then airtightly sealing them,or by interposing thermally meltable insulating films 46 between thefield core plates 43a and then thermally pressing them to integrallysolidify them and to keep a pressure-resistant and airtight state. Inaddition, a non-magnetic thin plate 47 or a resin thin film 47 is formedon the inner periphery of the stator core 43 by pressing so as to coverthe same, whereby the above-mentioned airtight state can be furtherimproved.

The above-mentioned stator core 43 is substantially cylindrical, andboth the ends of the stator core 43 in the axial direction areintegrally airtightly secured to a flange 48a of an outer frame housing48 airtightly fixed to the bearing housing 35 on the side of thecompressor A and a flange 28a of a mirror plate-like housing 28integrally associated with a bearing 29 on the free end side of therotating shaft 36.

According to the above-mentioned constitution, as just described, boththe ends of the stator core 43 are integrally secured to the outer framehousing 48 airtightly fixed to the side of the compressor A and themirror platelike housing 28 positioned on the free end side of therotating shaft 36, and therefore the stator core 43 can be utilized as apressure-resistant container by a cooperative function with thesemembers. Therefore, the stator core 43 can hold so sufficient pressureresistance as to withstand the refrigerating machine in which thecompression of the refrigerant gas is as high as 20 Kg/m².

On the other hand, the windings 45 received in the open grooves 44 ofthe stator core 43 are arranged in the same space as the rotor 41, andtherefore the working fluid composition containing the corrosive ammoniarefrigerant gets into the motor B through the incompletely sealed spacebetween the rotor shaft 37a of the compressor A and the bearing 34.Thus, it is necessary to subject the rotor 41 and the windings 45 to ananti-corrosive insulating treatment, but the anti-corrosive insulatingtreatment of the windings is very difficult.

Hence, as shown in FIG. 5(B), the open grooves 44 are filled with abinder resin 49 and insulating resin thin films 47 are then applied totheir inner peripheries to airtightly seal the open grooves 44.Alternatively, as shown in FIG. 5 (A), the open grooves 44 are filledwith the binder resin and seal plates 27 having both tapered sides aremounted on the opening ends of the open grooves 44. In this case, thepressure of the refrigerant gas in the container is applied to the backsurfaces of the seal plates 27 to airtightly seal the opening ends ofthe open grooves 44. As a result, the stator windings 44 in the opengrooves 12 are fixed and the opening surfaces of the open grooves areclosed, whereby tough mechanical strength, anti-corrosive properties andairtightness can be simultaneously held.

Possibility of Industrial Utilization

A lubricating oil and a working fluid composition for a refrigeratingmachine of the present invention have an excellent soluble stability toammonia and exert excellent lubricating properties under an ammoniarefrigerant atmosphere, and in addition, any solid is not formed duringthe operation of the refrigerating machine. Therefore, an oil recoverydevice which is necessary for a conventional refrigerating machine usingthe ammonia refrigerant can be omitted, which can be also applyed to asmall-sized refrigerator.

A refrigerating machine which is a second aspect of the presentinvention is constituted so that the working fluid compositioncomprising the lubricating oil and ammonia may be circulated through arefrigerating cycle or a heat pump cycle, whereby the constitution ofthe machine can be simplified and a heat transfer efficiency can beimproved. Hence, the industrially extremely advantageous refrigeratingmachine can be provided.

Particularly in preferable examples of the present invention, problemsof the insolubility of ammonia to the lubricating oil and corrosiveproperties of ammonia can be solved, whereby an ammonia enclosedcompressor can be easily provided, and its practical value is extremelylarge.

                  TABLE 1                                                         ______________________________________                                                 Structure or             Average                                              Type of Main    Random/  Molecular                                            Component Compound                                                                            Block    Weight                                      ______________________________________                                        Example 1                                                                              CH.sub.3 O(PO).sub.m CH.sub.3                                                                 --        800                                        Example 2                                                                              C.sub.4 H.sub.9 O(PO).sub.m (EO).sub.n CH.sub.3                                               Block     900                                                 (m:n = 8:2)                                                          Example 3                                                                              C.sub.8 H.sub.17 O(PO).sub.m (EO).sub.n CH.sub.3                                              Random    400                                                 (m:n = 9:1)                                                          Example 4                                                                              CH.sub.3 O(PO).sub.m (EO).sub.n CH.sub.3                                                      Block    1300                                                 (m:n = 7:3)                                                          Example 5                                                                              CH.sub.3 O(PO).sub.m CH.sub.3                                                                 --       1000                                        Example 6                                                                              CH.sub.3 O(PO).sub.m (EO).sub.n CH.sub.3                                                      Block    1000                                                 (m:n = 8:2)                                                          Example 7                                                                              CH.sub.3 O(PO).sub.m (EO).sub.n CH.sub.3                                                      Random   1000                                                 (m:n = 3:7)                                                          Example 8                                                                              Mixture of      (mixed)   850                                                 Example 3/Example 4 =                                                         50/50 (wt)                                                           ______________________________________                                                             Solubility                                                                    with Ammonia                                                                              Falex                                                 Kinematic   (phase      Seizure                                               Viscosity   separation  Load                                                  cst (100° C.)                                                                      temperature °C.)                                                                   Lbf (60° C.)                          ______________________________________                                        Example 1                                                                              7           -34         760                                          Example 2                                                                              9           -40         800                                          Example 3                                                                              3           -45         690                                          Example 4                                                                              14          -50 or less 860                                          Example 5                                                                              10          -15         780                                          Example 6                                                                              10          -50         820                                          Example 7                                                                              10          -50 or less 850                                          Example 8                                                                              6           -50 or less 800                                          ______________________________________                                               Condition before and after Bomb Test                                            Color       Total Acid Value                                                  (ASTM)      mgKoH/g     Appearance                                   ______________________________________                                        Example 1                                                                              L0.5/L0.5   0.01/0.01   Unchanged                                    Example 2                                                                              L0.5/L0.5   0.01/0.01   Unchanged                                    Example 3                                                                              L0.5/L0.5   0.01/0.01   Unchanged                                    Example 4                                                                              L0.5/L0.5   0.01/0.01   unchanged                                    Example 5                                                                              L0.5/L0.5   0.01/0.01   Unchanged                                    Example 6                                                                              L0.5/L0.5   0.01/0.01   Unchanged                                    Example 7                                                                              L0.5/L0.5   0.01/0.01   Unchanged                                    Example 8                                                                              L0.5/L0.5   0.01/0.01   Unchanged                                    ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                 Structure or    Average                                                       Type of Main    Random/   Molecular                                           Component Compound                                                                            Block     Weight                                     ______________________________________                                        Comparative                                                                            Naphthenic      --         400                                       Example 1                                                                              mineral                                                                       refrigerating oil                                                    Comparative                                                                            Branched alkyl  --         300                                       Example 2                                                                              benzene                                                              Comparative                                                                            C.sub.12 H.sub.25 O(PO).sub.m H                                                               --        1000                                       Example 3                                                                     Comparative                                                                            C.sub.4 H.sub.9 O(BO).sub.1 CH.sub.3                                                          --         600                                       Example 4                                                                     Comparative                                                                            C.sub.4 H.sub.9 O(PO).sub.m (EO).sub.n CH.sub.3                                               Random    1900                                       Example 5                                                                              (m:n = 8:2)                                                          Comparative                                                                            C.sub.12 H.sub.25 O(PO).sub.m CH.sub.3                                                        --        1000                                       Example 6                                                                     Comparative                                                                            CH.sub.3 O(PO).sub.m (EO).sub.n H                                                             Random    1800                                       Example 7                                                                              (m:n = 8:2)                                                          Comparative                                                                            CH.sub.3 O(PO).sub.m H                                                                        --        1000                                       Example 8                                                                     ______________________________________                                         BO: Oxybutylene                                                          

                         Solubility                                                                    with Ammonia                                                                              Falex                                                Kinematic    (phase      Seizure                                              viscosity    separation  Load                                                 Cst (100° C.)                                                                       temperature °C.)                                                                   Lbf (60° C.)                          ______________________________________                                        Comparative                                                                            5           Insoluble at                                                                              450                                          Example 1            room temperature                                         Comparative                                                                            4           Insoluble at                                                                              300                                          Example 2            room temperature                                                                          or less                                      Comparative                                                                           10           Insoluble at                                                                              780                                          Example 3            room temperature                                         Comparative                                                                            5           Insoluble at                                                                              820                                          Example 4            room temperature                                         Comparative                                                                           20           Insoluble at                                                                              830                                          Example 5            room temperature                                         Comparative                                                                           10           Insoluble at                                                                              770                                          Example 6            room temperature                                         Comparative                                                                           20           -50 or less 900                                          Example 7                                                                     Comparative                                                                           10           -50 or less 800                                          Example 8                                                                     ______________________________________                                                 Condition before and after Bomb Test                                            Color     Total Acid Value                                                    (ASTM)    mgKOH/g      Appearance                                  ______________________________________                                        Comparative                                                                              L0.5/L0.5 0.01/0.01    Unchanged                                   Example 1                                                                     Comparative                                                                              L0.5/L0.5 0.01/0.01    Unchanged                                   Example 2                                                                     Comparative                                                                              L0.5/--*  0.01/--      Unchanged                                   Example 3                                                                     Comparative                                                                              L0.5/L0.5 0.01/0.01    Unchanged                                   Example 4                                                                     Comparative                                                                              L0.5/L0.5 0.01/0.01    Unchanged                                   Example 5                                                                     Comparative                                                                              L0.5/L0.5 0.01/0.01    Unchanged                                   Example 6                                                                     Comparative                                                                              L0.5/--*  0.01/--      Solidified                                  Example 7                                                                     Comparative                                                                              L0.5/--*  0.01/--      Solidified                                  Example 8                                                                     ______________________________________                                         *White (by observation)                                                  

                  TABLE 3                                                         ______________________________________                                                Characteristics                                                               Solubility °C.                                                         (phase                                                                        separation  Fluidity (sec)                                            Oil       temperature)  -30° C.                                                                        -50° C.                                ______________________________________                                        Naphthenic                                                                              Separated     103     300 or more                                   Mineral Oil                                                                             at Room                                                                       Temperature                                                         Example 6 -50           1 or less                                                                             4.5                                           ______________________________________                                         Notes:                                                                        Solubility: NH.sub.3 (1 ml) was added to the oil (5 ml) at a room             temperature (a glass tube having a diameter of 11 mm), the mixture was        cooled at 2-3° C./minute, and then the phase separation temperatur     was measured.                                                                 Fluidity: A sample (above glass tube for measuring solubility) was shaken     at 0° C. for 1 minute, then keeped for 1 hour on a bath at             0° C. (vertically), after that cool down to measuring temperature      then maintained 30 minutes (vertically), and after vertically inverted, a     time taken until the oil flowed 50 mm was measured.                      

We claim:
 1. A working fluid composition for a refrigerating compressorusing ammonia as a refrigerant which comprises a mixture of ammonia andat least 2% by weight of one or more polyether compounds having anaverage molecular weight of 300 to 1,800, said polyether compounds beingrepresented by the formula (I)

    R.sub.1 -- --O--(PO).sub.m --(EO).sub.n --R.sub.2 !.sub.x  (I)

wherein R₁ is a hydrocarbon group having 1 to 6 carbon atoms, R₂ is analkyl group having 1 to 6 carbon atoms, PO is an oxypropylene group, EOis an oxyethylene group, x is an integer of from 1 to 4, m is a positiveinteger, and n is 0 or a positive integer.
 2. The working fluidcomposition according to claim 1 wherein the number of the total carbonatoms of R₁ and R₂ in the formula (I) is 10 or less.
 3. The workingfluid composition according to claim 2 wherein each of R₁ and R₂ in theformula (I) is independently an alkyl group having 1 to 4 carbon atoms.4. The working fluid composition according to claim 3 wherein each of R₁and R₂ in the formula (I) is independently a methyl group or an ethylgroup, and x is
 1. 5. The working fluid composition according to claim 1wherein R₁ is a hydrocarbon group having 1 to 4 carbon atoms, and R₂ isan alkyl group having 1 to 4 carbon atoms, and x is from 2 to
 4. 6. Theworking fluid composition according to claim 1 wherein in the formula(I), a ratio of m/(m+n) is from 0.5 to 1.0.
 7. The working fluidcomposition according to claim 1 wherein R₁ in the formula (I) is amethyl group.
 8. The working fluid composition according to claim 1wherein ultrafine diamond having an average particle diameter of about150 Å or less is added to the working fluid composition.
 9. An ammoniarefrigerating machine characterized by constituting a refrigeratingcycle or a heat pump cycle containing a refrigerant compressor, acondenser, an expansion valve and an evaporator, ammonia and at least 2%by weight of one or more polyether compounds having an average molecularweight of 300 to 1,800, said polyether compounds being represented bythe formula (I)

    R.sub.1 -- --O--(PO).sub.m --(EO).sub.n --R.sub.2 !.sub.x  (I)

wherein R₁ is a hydrocarbon group having 1 to 6 carbon atoms, R₂ is analkyl group having 1 to 6 carbon atoms, PO is an oxypropylene group, EOis an oxyethylene group, x is an integer of from 1 to 4, m is a positiveinteger, and n is 0 or a positive integer.
 10. A method for lubricatinga refrigerating compressor which is characterized by lubricating theammonia refrigerant compressor with a lubricating oil comprising atleast 2% by weight of one or more ether compounds having an averagemolecular weight of 300 to 1,800, said polyether compounds beingrepresented by the formula (I)

    R.sub.1 -- --O--(PO).sub.m --(EO).sub.n --R.sub.2 !.sub.x  (I)

wherein R₁ is a hydrocarbon group having 1 to 6 carbon atoms, R₂ is analkyl group having 1 to 6 carbon atoms, PO is an oxypropylene group, EOis an oxyethylene group, x is an integer of from 1 to 4, m is a positiveinteger, and n is 0 or a positive integer.
 11. The method forlubricating an refrigerating compressor according to claim 10 whereinthe number of the total carbon atoms of R₁ and R₂ in the formula (I) is10 or less.
 12. The method for lubricating an refrigerating compressoraccording to claim 10 wherein each of R₁ and R₂ in the formula (I) isindependently an alkyl group having 1 to 4 carbon atoms.
 13. The methodfor lubricating an refrigerating compressor according to claim 10wherein each of R₁ and R₂ in the formula (I) is independently a methylgroup or an ethyl group, and x is
 1. 14. The method for lubricating arefrigerating compressor according to claim 10 wherein R₁ is ahydrocarbon group having 1 to 4 carbon atoms, and R₂ is an alkyl grouphaving 1 to 4 carbon atoms, and x is from 2 to 4.